Outside of an unexpected exception here or there, we pretty much know which teams have lost which players for the 2013 season via free agency or trades.

While the trades are self-inflicted wounds for the most part, wounds that won't be bandaged up unless and until prospects fulfill their potential, some teams believe they are better off in the long run without free agents they elected not to re-sign. And for the most part, they might be correct.

However, we aren't talking about the long-term right now. When we discuss the five most irreplaceable players in the major leagues going into next season, we are strictly talking about the next season, and maybe the one after that, before draft picks and prospects have a chance to bloom.

1. Zack Greinke, SP

Two teams find themselves replacing Greinke in 2013, and that's part of the reason he tops this list. The Milwaukee Brewers likely won't contend in the National League Central because they are missing Greinke, and the Los Angeles Angels—who traded for Greinke before the July 31 non-waiver deadline—can't be called the clear favorites in the American League West because they couldn't re-sign him.

Not only that, but losing Greinke doesn't come with a compensation pick because he was traded during last season. So when the Los Angeles Dodgers signed him for $147 million over six years, neither the Brewers nor the Angels saw an extra pick come their way.

But Greinke isn't valuable only because he's not tied to draft-pick compensation. He's simply been one of baseball's best right-handed starters over the last four years. He's compiled a 23.5 WAR, according to fangraphs.com, and that is fifth-best in the majors behind Felix Hernandez, Roy Halladay, Cliff Lee and Justin Verlander. Greinke is ahead of CC Sabathia, Clayton Kershaw, Jon Lester, Dan Haren and Tim Lincecum over that span.

Over the last two seasons, Greinke is third in the majors with 9.4 strikeouts per nine innings, sixth in Fielding Independent Pitching (3.05) and second in expected FIP.

Greinke might not be a true ace, but the Dodgers already have one of those, making Greinke possibly the best No. 2 starter in the game.

2. Josh Hamilton, OF

Hamilton was the best position player on the market and by the end of the 2013 season, losing him will hurt more than losing any other position player. The Texas Rangers' offense still should be good despite losing a guy who posted a .305/.363/.549 slash line with a .912 OPS, 136 OPS-plus and an AL MVP Award over the last three seasons.

But the effect will be felt in part because the Angels again are playing the card that makes them stronger and weakens the rival Rangers.

Signing C.J. Wilson and trading for Greinke also did that, or at least we believed that to be so at the time of those acquisitions.

Losing Hamilton truly weakens the Rangers considering Hamilton has a 22.4 WAR, according to fangraphs.com, over the last five seasons, which is good for ninth in the AL. He is also fifth in home runs (142) over that span, eighth in average (.305), third in slugging percentage (.549), third in OPS

(.912) and fourth in weighted on-base average (.386).

Those numbers pretty much speak for themselves. Hamilton is one of the true heart-of-the-order bats in the majors, and since the Rangers haven't been able to land a front-line pitcher or pull off anything for a guy like Justin Upton or a free agent, losing Hamilton hurts that much more.

3. R.A. Dickey, SP

The New York Mets likely were not going to compete in the National League East even if they had the reigning Cy Young Award winner heading their rotation. So calling him one of the game's most irreplaceable players sort of goes back to the 2011 NL MVP race when Ryan Braun beat out Matt Kemp despite Kemp having better numbers. Kemp's team wasn't in the playoff race, so Braun won. Ipso facto, Dickey can't be that irreplaceable.

Well, I don't subscribe to the belief that Kemp wasn't the most valuable player in 2011, so I don't subscribe to Dickey being less valuable because he played for the Mets. The bottom line is he is among the most important/best players to switch teams this offseason, and with starting pitching being so valuable in today's market, his loss is that much more damaging.

Over the last three seasons, Dickey is 39-28 with a 2.95 ERA, 466 strikeouts, a 3.13 strikeout-to-walk ratio, 1.15 WHIP and a 129 ERA-plus.

That makes him one of the best starters in the league since the start of the 2010 season, and he is a huge reason why the Toronto Blue Jays are now considered the favorites in the American League East.

If you thought the Mets were bad last season (74-88), wait until you see them without one of the best starting pitchers the game has to offer.

4. B.J. Upton, CF

Upton has been compared to Michael Bourn all offseason, but the fact is the Tampa Bay Rays will miss Upton far more than the Atlanta Braves will miss Bourn (because the Braves signed Upton is the No. 1 reason). While Bourn is a stellar center fielder, Upton is good enough to assure the Braves don't cry over losing Bourn's glove. And Upton's power—51 home runs and 56 doubles over the last two years—will dwarf Bourn's, so as you can see, Bourn is already replaced in Atlanta.

Not only that, but the Braves are in a much better position to compete in their division than the Rays are in theirs. That sort of shoots down my thoughts on Dickey being irreplaceable but only to a certain extent because the Rays actually did compete in their group last season and losing Upton is a reason they might not in 2013.

5. Melky Cabrera, OF

Before San Francisco Giants fans, or whoever, get all crazy about Cabrera being on this list, remember that the Giants are now expected to use a platoon of Gregor Blanco and Andres Torres in left field. Those guys had 95 and 85 OPS-pluses, respectively, last season. Cabrera had a career-high 158 OPS-plus in 113 games last year before he was suspended in August for testing positive for synthetic testosterone.

The Giants played well after his suspension and went on to win their second World Series in three seasons, but his impact up until he was banned can't be ignored. He was one of the best hitters in the majors to that point and was a big reason the Giants were in first place.

It's possible Cabrera tanks next season with the Blue Jays, but it's also possible he doesn't and that the Blanco-Torres platoon can't produce better than a replacement-level player. And with the Dodgers doing all they can to catch their biggest rivals, the Giants need all the help they can get to stay on top.